1. Field of the Invention
The present invention relates generally to an optical storage device, and more particularly to an optical pickup unit in an optical disk drive.
2. Description of the Related Art
An optical disk has received attention as a memory medium that becomes a core in the recent rapid development of multimedia, and it is usually accommodated in a cartridge case to be provided as an optical disk cartridge for practical use. The optical disk cartridge is loaded into an optical disk drive to perform reading/writing of data from/to the optical disk by means of an optical pickup (optical head).
A recent optical disk drive intended to realize size reduction is composed of a fixed optical assembly including a laser diode module, a beam splitter for reflecting and transmitting a laser beam, and a photodetector for receiving reflected light from an optical disk, and a movable optical assembly including a carriage and an actuator mounted on the carriage and having an objective lens. The carriage is movable in the radial direction of the optical disk along a pair of rails by means of a voice coil motor.
A write-power laser beam emitted from the laser diode of the fixed optical assembly is first collimated by a collimator lens, next transmitted by the beam splitter, next reflected by a beam raising mirror of the movable optical assembly, and finally focused on the optical disk by the objective lens, thereby writing data onto the optical disk. On the other hand, data reading is performed by directing a read-power laser beam onto the optical disk. Reflected light from the optical disk is first collimated by the objective lens, next reflected by the beam splitter, and finally detected by the photodetector, thereby converting the detected optical signal into an electrical signal.
The actuator includes an actuator base (fixed portion) fixed to the carriage, and a lens holder (movable portion) supported to the actuator base in a cantilever fashion by a plurality of spring wires or leaf springs. The lens holder has an objective lens, a focusing coil, and a plurality of tracking coils. A magnetic circuit opposed to the focusing coil and the tracking coils to configure a voice coil motor (VCM) is fixed to the actuator base or the carriage.
In the conventional optical disk drive, the light beam emitted from the light source in a direction substantially parallel to the recording surface of the optical disk is reflected in a direction perpendicular to the recording surface of the optical disk by the beam raising mirror, and next focused on the recording surface of the optical disk by the objective lens supported to the actuator. In this configuration, the objective lens is moved in a direction perpendicular to the recording surface of the optical disk by passing a current through the focusing coil, thereby performing a focusing operation.
Accordingly, the height of the optical pickup unit is equal to the sum of the height of the beam raising mirror and the height of the actuator. Actually, it is also necessary to ensure a movable range of the objective lens in the focusing direction. Accordingly, the height of the optical pickup unit can be reduced only by reducing the size of each component including the diameter of the light beam in the conventional optical disk drive. As a result, there is a limit to the reduction in thickness of the optical pickup unit.
In the conventional optical disk drive, the position of the actuator (the movable portion) is detected by using a two-segment photodetector or a four-segment photodetector to detect a part of the light beam emitted from the light emitting element mounted on the carriage and shielded by a light shielding portion provided on the movable portion of the actuator. Thus, the light emitting element and the photodetector must be mounted on the carriage to detect the position of the actuator in the tracking direction and the focusing direction in the conventional optical disk drive, causing an increase in size of the optical pickup unit. Furthermore, since the light shielding portion is required in the actuator, physical symmetry in the actuator is marred and it is therefore difficult to ensure good dynamic characteristics.
It is therefore an object of the present invention to provide an optical storage device which can realize a reduction in thickness of the optical pickup unit.
It is another object of the present invention to provide an optical storage device which can ensure physical symmetry in the optical pickup unit.
In accordance with an aspect of the present invention, there is provided an optical storage device capable of at least reading information recorded on an optical storage medium, including a drive base; a carriage mounted on the drive base so as to be reciprocatable in a first direction; first driving means for moving the carriage; a light source mounted on the drive base; a first lens fixed to the carriage for focusing a light beam emitted from the light source onto the optical storage medium; a second lens interposed between the first lens and the light source for focusing the light beam onto the optical storage medium in cooperation with the first lens; a beam splitter for reflecting at least a part of the light beam transmitted through the second lens in a direction perpendicular to the optical storage medium; and an actuator for supporting the second lens so that the second lens is movable in a given direction. The actuator includes an actuator base mounted on the carriage; a lens holder for holding the second lens so that the optical axis of the second lens extends in a direction substantially parallel to the optical storage medium; a supporting means for movably supporting the lens holder to the actuator base; and a second driving means for moving the second lens in the given direction. The second driving means includes a magnetic circuit fixed to the actuator base and a plurality of coils fixed to the lens holder.
The given direction includes the same direction as the first direction, and the second lens is moved in the first direction to thereby perform focusing of a beam spot formed on the optical storage medium in cooperation with the first lens. The given direction includes a rotational direction about an axis substantially perpendicular to the first direction and substantially parallel to the optical storage medium, and the second lens is rotated about the axis to thereby perform tracking of the beam spot formed on the optical storage medium.
Preferably, the optical storage device further includes a photodetector for detecting a light beam transmitted by the beam splitter. The photodetector may be a six-segment photodetector, and an output from each segment of the photodetector is differentially detected to thereby detect the position of the actuator in a focusing direction and a tracking direction.
According to the optical storage device of the present invention, the second lens supported by the actuator is moved in a direction substantially parallel to the optical storage medium to thereby perform the focusing operation, so that the thickness of the optical pickup unit can be reduced.
In accordance with another aspect of the present invention, there is provided an optical pickup unit capable of at least reading information recorded on an optical storage medium, including a light source; a carriage reciprocatable in a first given direction; a first lens fixed to the carriage for focusing a light beam emitted from the light source onto the optical storage medium; a second lens interposed between the first lens and the light source for focusing the light beam onto the optical storage medium in cooperation with the first lens; a beam splitter for reflecting at least a part of the light beam transmitted through the second lens in a direction perpendicular to the optical storage medium; and an actuator for supporting the second lens so that the second lens is movable in a second given direction. The actuator includes an actuator base mounted on the carriage; a lens holder for holding the second lens so that the optical axis of the second lens extends in a direction substantially parallel to the optical storage medium; a supporting means for movably supporting the lens holder to the actuator base; and a driving means for moving the second lens in the second given direction. The driving means includes a magnetic circuit fixed to the actuator base and a plurality of coils fixed to the lens holder.
The above and other objects, features and advantages of the present invention and the manner of realizing them will become more apparent, and the invention itself will best be understood from a study of the following description and appended claims with reference to the attached drawings showing some preferred embodiments of the invention.